Independent control of two solenoid operated valves over two wires in an irrigation system

ABSTRACT

Apparatus  11  and  13  for interfacing two AC sources with two AC loads  17   a    17   b  in the form of solenoid operated valves over a single conductor  25 , with a return conductor  19  in an irrigation system is disclosed. The apparatus has an encoder circuit  11  with two inputs  21   a    21   b  for connection to the two AC sources, and an output  23  for connection to the single conductor  25 , and a decoder circuit  13  having an input  27  for connection to the conductor  25 , and two outputs  29   a    29   b  for connection to loads  17   a    17   b  respectively. When the first input  21   a  is powered, the first load  17   a  will be switched on, and when the second input  21   b  is powered, the second load  17   b  will be switched on. The decoder portion  13  incorporates switching circuits  43   a    43   b , interfaced with turn on delay timers  45   a    45   b  respectively, to delay operating the loads at switch on, and turn-off delay timers  47   a    47   b  to hold the loads on after switch off.

FIELD OF THE INVENTION

This invention relates to a duplexing encoder/decoder pair foralternating current systems, in general, and to a system for operatingtwo loads independently, from two independent current sources and asingle return, while using two conductors to connect the current sourcesand return to the loads, in particular. The invention has particular,but not exclusive, application in the field of automatic sprinklersystems comprising a number of solenoid valves electrically connected toan irrigation controller for the timing and switching thereof.

Throughout the specification unless the context requires otherwise, theword “comprise” or variations such as “comprises” or “comprising”, willbe understood to imply the inclusion of a stated integer or group ofintegers but not the exclusion of any other integer or group ofintegers.

Throughout the specification unless the context requires otherwise, theword “include” or variations such as “includes” or “including”, will beunderstood to imply the inclusion of a stated integer or group ofintegers but not the exclusion of any other integer or group ofintegers.

BACKGROUND ART

The following discussion of the background art is intended to facilitatean understanding of the present invention only. It should be appreciatedthat the discussion is not an acknowledgement or admission that any ofthe material referred to was part of the common general knowledge as atthe priority date of the application.

The solenoid valves utilized in such automatic sprinkler systems requireenergization of the solenoid to operate the valve. Most solenoids usedin this application are actuated and held by a 24 volt AC currentsupplied by the irrigation controller. Typically, one conductor (common)is required to connect each load (solenoid) to each switched currentsource (output) of the irrigation controller, and one conductor isrequired to connect the return from all of the loads to the irrigationcontroller.

In an existing automatic sprinkler system installation, the solenoidoperated valves are usually located below ground, and electrical cablingconnecting the solenoid operated valves to a reticulation controllerwill usually be buried underground. When it is desired to add anadditional solenoid operated valve, usually there will not be sufficientcabling as the system will have been originally installed with only therequired cabling, and without any capacity for expansion.

A previous attempt has been made to operate two independent AC loadsfrom two independent current sources and a return utilizing twoconductors to interconnect the current sources and return with thealternating current loads. This product is manufactured by TransitionalSystems Manufacturing Company of West Sacramento, Calif., under thetrademark “Doubler” and is described in U.S. Pat. No. 4,575,004. Theapparatus described in U.S. Pat. No. 4,575,004 is a complex mechanicaldevice incorporating latching switching means, viz. electromechanicallatching relays. When this apparatus is used it increases the electricalload on the circuit over and above that formerly presented by thesolenoid or solenoids connected in parallel to the irrigationcontroller. Moreover, such electromechanical relays are subject tomalfunction and/or failure over extended periods of time. In addition,the apparatus described in U.S. Pat. No. 4,575,004 cannot be used toswitch between two alternating current loads connected thereto unlessthere is a delay between the first alternating current load beingswitched off and the second alternating current load being energized.Thus, in most modern irrigation controllers, the apparatus described inU.S. Pat. No. 4,575,004 could not be used to switch between adjacentoutputs to solenoid valves in the switching sequence of the irrigationcontroller.

Another system for operating two independent AC loads from twoindependent current sources and a return utilizing two conductors tointerconnect the current sources and return with the alternating currentloads is described in U.S. Pat. No. 5,780,938. A difficulty with thissystem is that with modern irrigation controllers incorporatingmonitoring of outputs to solenoid valves, this has resulted in outputscutting out due to over-current, or outputs being skipped, due to theirrigation controller falsely detecting a fault condition.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a device which overcomes theaforementioned difficulties.

In accordance with one aspect of the present invention there is providedapparatus to allow independent control of a first load and a second loadin the form of solenoid operated valves in an irrigation system via asingle conductor with a single common return. The apparatus comprises anencoder circuit locatable in use proximal to an irrigation controller,and a decoder circuit locatable adjacent to said solenoid operatedvalves, the encoder circuit having a first input for connection to afirst irrigation controller output, and a second input for connection toa second irrigation controller output, and an output for connection tothe single conductor. The apparatus also comprises a decoder circuithaving an input for connection to the single conductor, a first outputfor connection to the first load and a second output for connection tothe second load. When the first input is energised, the first outputwill be energised, and when the first input is de-energised the firstoutput will be de-energised and when the second input is energised, thesecond output will be energised, and when the second input isde-energised the second output will be de-energised.

The decoder circuit also incorporates a first switching circuit betweensaid input and said first output, interfaced with a first turn on delaytimer to time out a predetermined period before operating said firstswitching circuit, and a second switching circuit between said input andsaid second output, interfaced with a second turn on delay timer to timeout a predetermined period before operating said second switchingcircuit.

In this manner, viewing the circuit arrangement current flow using theconventional current convention, a positive going voltage at the firstdecoder input will be available at the first decoder output but onlyafter the predetermined period has timed out, and a negative goingvoltage at the second encoder input will be available at the seconddecoder output but only after the predetermined period has timed out.Conversely, negative going voltage at the first encoder input and apositive going voltage at the second encoder input will be blocked. Aswill be appreciated, a return conductor will be required between theloads and the return of the current supply.

The first decoder output and the second decoder output each includeassociated therewith a turn-off delay circuit. Alternatively, theturn-off delay circuit may be associated with the load, or turn-offdelay may be inherent in the physical design of the load, particularlywhere the load is inductive. In one arrangement the first decoder outputand the second decoder output each include an inductive turn-off delaycircuit. In a preferred embodiment the turn-off delay circuit comprisesfrom each output to common, an LC snubber circuit.

In a particularly preferred and advantageous arrangement each turn-offdelay circuit comprises a diode and capacitor connected in parallel,connected in series with an inductor, which when in circuit is connectedacross the load which is connected to the relevant output.

For a solenoid operated valve which is intended to operate on 24 voltsAC, the value of the capacitor can range from 4.7 μF to 22 μF and thevalue of the inductor can range from 50 μH to 300 μH. Generally, thehigher value the capacitor is, the higher value of inductor is used.Typically, where a capacitor of 10 μF is used, an inductor of 100 μH issuitable. The turn-off delay circuit preferably delays turn off of therelevant output by holding the output high for a period of at least0.015 seconds. Preferably the turn-off delay circuit delays turn off ofthe relevant output by holding the output high for a period of at least0.015 seconds. While the turn off delay could be longer, this wouldincrease the probability of two outputs being operational at the sametime, which could interfere with operation of a reticulation system,especially where there is low pressure monitoring and trip out.

The first switching circuit and the second switching circuit eachpreferably use a low gate current triac. Typical gate currents may beless than 15 mA, or preferably less than about 10,A. The low gatecurrent triac is preferably capable of switching with gate currents aslow as 5 mA. Preferably the low gate current triac can switch in allfour quadrants.

The first turn on delay timer to time out a predetermined period beforeoperating said first switching circuit and the second turn on delaytimer to time out a predetermined period before operating said secondswitching circuit may each be a transistor based RC timer circuit.

Preferably the first turn on delay timer and the second turn on delaytimer each provide a turn on delay of at least 0.1 seconds, and mostpreferably a turn on delay of about 0.5 seconds. This equates to five 50Hz cycles or six 60 Hz cycles as a minimum, and 25 50 Hz cycles or 30 60Hz cycles as an optimum. While the turn on delay could be longer, thisincreases the time that an output might not be operating, which in anirrigation application may interfere with normal operation, especiallyif there is high pressure trip out protection, for example.

Preferably the duplex encoder/decoder pair employs diode means tocontrol the conduction direction of electrical current therethrough.

In accordance with a second aspect of the invention there is provided adecoder half for a duplex decoder, for use with a duplex encoder, saidduplex decoder half having an input connecting to a half wave rectifierhaving a half wave rectified output, said half wave rectified outputleading to a switching circuit interfaced with a turn on delay timer totime out a predetermined period before operating said switching circuiton said half wave rectifier passing current at an operational voltage,the output of the switching circuit connecting to an output forconnecting to a load and to a turn-off delay circuit.

In accordance with a third aspect of the invention there is provided, anirrigation system solenoid operated valve control circuit, said controlcircuit having an input connecting to a half wave rectifier having ahalf wave rectified output, said half wave rectified output leading to aswitching circuit interfaced with a turn on delay timer to time out apredetermined period before operating said switching circuit on saidhalf wave rectifier passing current at an operational voltage, theoutput of the switching circuit connecting to an output for connectingto a solenoid of said solenoid operated valve, where the output includesassociated therewith a turn-off delay circuit.

The turn off delay circuit may advantageously be an inductive turn-offdelay circuit, and in a more preferred embodiment the turn-off delaycircuit comprises from the output to common, an LC snubber circuit.

In a particularly preferred and advantageous arrangement the turn-offdelay circuit comprises a diode and capacitor connected in parallel,connected in series with an inductor, which when in circuit is connectedacross the load which is connected to the relevant output.

For a solenoid operated valve which is intended to operate on 24 voltsAC, the value of the capacitor can range from 4.7 μF to 22 μF and thevalue of the inductor can range from 50 μH to 300 μH. Generally, thehigher value the capacitor is, the higher value of inductor is used.Typically, where a capacitor of 10 μF is used, an inductor of 100 μH issuitable. The turn-off delay circuit preferably delays turn off of therelevant output by holding the output high for a period of at least0.015 seconds. Preferably the turn-off delay circuit delays turn off ofthe relevant output by holding the output high for a period of at least0.015 seconds. While the turn off delay could be longer, this wouldincrease the probability of two outputs being operational at the sametime, which could interfere with operation of a reticulation system,especially where there is low pressure monitoring and trip out.

The switching circuit preferably uses a low gate current triac. This lowgate current triac is preferably capable of switching with gate currentsas low as 5 mA. Preferably the low gate current triac can switch in allfour quadrants.

The turn on delay timer to time out a predetermined period beforeoperating said switching circuit may be a transistor based RC timercircuit.

Preferably the turn on delay timer provides a turn on delay of at least0.1 seconds, and most preferably a turn on delay of about 0.5 seconds.This equates to five 50 Hz cycles or six 60 Hz cycles as a minimum, and25 50 Hz cycles or 30 60 Hz cycles as an optimum. While the turn ondelay could be longer, this increases the time that an output may not beoperating, which in an irrigation application may interfere with normaloperation, especially if there is high pressure trip out protection, forexample.

In accordance with another aspect of the present invention, there isprovided a method of independently controlling two loads connected totwo power supplies by a source conductor and a return conductor,comprising connecting an encoder portion as described above between asource conductor and the power supplies, and connecting a decoderportion as described above between a source conductor and the loads.

In accordance with a further aspect of the invention, there is provideda method of independently controlling two loads connected to twoalternating current power supplies by a source conductor and a returnconductor. The method and apparatus comprises allowing only the positivegoing voltage from one power supply to reach one load while blocking thenegative going voltage from the one power supply reaching the sourceconductor. Conversely, this method and apparatus comprises allowing onlythe negative going voltage from a second power supply to reach a secondload while blocking the positive going voltage from reaching the sourceconductor. Also, the method prevents negative going voltage fromreaching the one load from the source conductor and preventing positivegoing voltage from reaching the other load from the source conductor.The method provides a turn on delay for each of the first and secondloads, and a turn-off delay for each of the first and second loads.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention being a duplexencoder/decoder pair for controlling separate operation of two solenoidoperated valves over two wires will now be described with reference tothe drawings in which:

FIG. 1 is a block schematic showing a duplex encoder/decoder pair forcontrolling separate operation of two solenoid operated valves over twowires;

FIG. 2 is a block schematic showing circuits present in the duplexdecoder circuit of the embodiment; and

FIG. 3 is a circuit diagram of duplex encoder/decoder pair.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

The invention is described relative to a specific embodiment thereofgiven with reference to the drawing which is a circuit schematic of aduplex encoder/decoder pair for use in an automatic sprinkler system forwatering gardens, lawns and the like. The particular application isdirected to the addition of an additional watering zone controlledthrough an additional solenoid operated valve, to an existing systemwithout the necessity of extensive digging and/or trenching to runcontrol wires. Other applications of the system are contemplated.

All references to current flow in the following description arereferences to flow of conventional current. That is, current flow isfrom a higher to a lower potential, including from a higher positivepotential to a lower positive potential or a negative potential, or froma less negative potential to a more negative potential.

The embodiment is directed towards a duplexing encoder/decoder paircomprising an encoder circuit 11 and a decoder circuit 13 connectedbetween an irrigation controller 15 and first and second loads in theform of solenoid valves 17 a and 17 b, respectively. Typically, one ofthe solenoid valves, e.g. valve 17 a, is in place while the othersolenoid valve, e.g. valve 17 b, is to be added. Solenoid valve 18 whichwas already in place, is shown connected to station output 1, butotherwise plays no part in the embodiment.

Referring to the irrigation controller 15 only the water zone or stationoutput current sources for stations 1-5 inclusive are shown, togetherwith the connection C for the return conductor 19. Other portions of atypical controller are omitted from this description for convenience.

The encoder circuit 11 has its inputs 21 a and 21 b connected to stationoutputs 2 and 3 of the irrigation controller 15. The station outputs 2and 3 represent current sources connected thereto. The output 23 of theencoder circuit 11 is connected to one end of a single conductor 25which would have been, prior to modification of the irrigation system,typically connected already to the existing solenoid 17 a.

The other end of conductor 25, in this system is re-connected to thesingle input 27 of decoder circuit 13. The decoder circuit 13 has twooutputs 29 a and 29 b which are connected to the solenoid valves 17 aand 17 b, respectively. The decoder circuit 13 also has a commonconnection 31 which is connected to the return conductor 19 togetherwith the return connections of the solenoid valves 17 a and 17 b.

In a preferred embodiment, the encoder circuit 11 comprises a pair ofdiodes 33 a and 33 b. Diode 33 a has the cathode thereof connected toinput 21 a. Conversely, diode 33 b has the anode thereof connected toinput 21 b. The other terminals of diodes 33 a and 33 b are connectedtogether and to the encoder output 23.

Similarly, the decoder circuit 13 comprises two half wave rectifiers 34each in the form of a diode 35 a and 35 b connected in a similar fashionto the diodes 33 a and 33 b. Diode 35 a has its cathode connected to theanode of diode 35 b and connected to input 27 of decoder circuit 13 viaa 1 amp poly fuse 36, and a 27 volt 7 mm varistor 37 which acts as avoltage clamp to dissipate any voltage spikes that reach the decodercircuit 13. The poly fuse heats up when a fault occurs and increasesit's internal resistance until the load becomes balanced. Once the faultis removed the poly fuse cools down and again allows current to flow.The varistor is used to clamp the input cable 25 and to capture anypower spikes before they enter the decoder. The varistor also acts as aterminator for the field cable 25 and helps with lightning and otherconduction that would normally cause failure of the irrigationcontroller.

In conventional fashion, the irrigation controller 15 provides timingand switching of, typically, 24 volts AC at any one of the terminals 1through 5 (or more, not shown). The AC voltage is measured betweenrespective terminals and the common connection C. When 24 volts AC isprovided between terminal 2 and common connection C, the voltage is halfwave rectified by diode 33 a to produce a voltage waveform the encoderoutput 23 which is at negative potential relative to the returnconductor 19. This voltage is supplied to decoder 13 via conductor 25.In the decoder circuit 13 the diode 35 a conducts, resulting a negativevoltage being available at half wave rectifier 34 output 39 a.

Conversely, when 24 volts AC appears between terminal 3 and commonconnection C, this voltage signal is half wave rectified by diode 33 bto produce a positive potential at the encoder output 23 relative to thereturn conductor 19. This voltage is supplied to decoder 13 viaconductor 25. Thus, the diode 35 b is rendered conductive, resulting ina positive voltage being available at half wave rectifier 34 output 39b.

The decoder 13 comprises two mirror circuits being a positive halfdecoder circuit 13 b and a negative half decoder circuit 13 a.

The output 39 a of the half wave rectifier 34 formed by diode 35 a isconnected to a DC voltage regulator 41 a and to a switching circuit 43 aformed by a triac Q1. The DC voltage regulator 41 a is formed byresistors R1, R2, capacitor C1 and zener diode D4. The DC voltageregulator 41 a supplies a ten volt reference voltage to a turn-on timercircuit 45 a formed by transistor Q2, resistor R4, capacitor C2 and ared light emitting diode D5.

Similarly the output 39 b of the half wave rectifier 34 formed by diode35 b is connected to a DC voltage regulator 41 b and to a switchingcircuit 43 b formed by a triac Q3. The DC voltage regulator 41 b isformed by resistors R1, R6, capacitor C5 and zener diode D8. The DCvoltage regulator 41 b supplies a ten volt reference voltage to aturn-on timer circuit 45 b formed by transistor Q4, resistor R8,capacitor C6 and a red light emitting diode D9.

The triacs forming the switching circuits 43 a and 43 b are Z0409MFtypes, which are low gate current 4 amp triacs. These triacs are alittle unusual in that in all quadrants they switch at 5 mA gatecurrent. This is a useful property, allowing the decoder circuit formedby both triacs and associated parts to use all four quadrants to switch.For equal switching times it is important to be able to maintain equalswitching currents.

When power is supplied at the output 39 b or 39 a of either half waverectifier 34, in the turn on timer circuits 45 a and 45 b, the red lightemitting diode D5 or D9 passes a known current when reverse biased. Thiscurrent is used to control the charging of capacitor C2 or C6. When thevoltage at the base of transistor Q4 reaches −0.6V to that of thevoltage on the emitter of transistor Q4, transistor Q4 starts to conductand turns on the triac 43 a. Similarly, when the voltage at the base oftransistor Q2 reaches +0.6V to that of the voltage on the emitter oftransistor Q2, transistor Q2 starts to conduct and turns on the triac 43b.

This timer circuit 45 a or 45 b with the components illustrated and inparticular with the capacitor values shown, results in a turn-on delayof about half a second from when power is supplied to input 27 to thetime that the relevant triac switching circuit 43 a or 43 b turns on.

A turn-off delay circuit 47 a is formed by inductor L4, capacitor C7 anddiode D10 and is in circuit across the output 29 a and the common C orreturn, and in circuit across the coil L3 of the solenoid valve 17 a.Similarly, a turn-off delay circuit 47 b is formed by inductor L2,capacitor C4 and diode D6, in circuit across the output 29 a and thecommon C or return, in circuit across the coil L1 of the solenoid valve17 b.

The turn-off delay circuits 47 a and 47 b function as both a smoothingnetwork for the DC signal passed through Triac Q1 and also a snubbernetwork that clamps and dissipates the energy that is held in the coilsL3 and L1 of the solenoid valves 17 a or 17 b when the power is removed.This is important as the triac Q3 or Q1 is latched hard on, and becauseit is bi directional the collapsing field of the coil L3 or L1 of thesolenoid valves 17 a or 17 b can pass through the triac Q3 or Q1 whenthe power is removed and cause high inverted currents to exist in theconductor 25. These high signals can cause electronic fuses to trip andmake it difficult for channels of the two up to be side by side.

When power is switched by the triac Q1, the triac passes half wave DCthrough L2 and charges up C4, in addition to actuating coil L1 of thesolenoid valve 17 b. This LC network of L2 and C4 provides enoughsmoothing so that the half wave signal being applied to the 24 VAC coilL3 of the solenoid valve 17 b does not chatter.

A 27 volt varistor 49 b is provided across the turn off delay circuit 47b and across the coil L1 of the solenoid valve 17 b to capture any highcurrent pulses that occur when the current to coil L1 turns off and thecoil field collapses. All other field currents below the varistorsclamping voltage are loaded into L2 and used to hold the charge incapacitor C4. Doide D6 which is in parallel with capacitor C4 acts as afree wheeling diode. When the station 3 of the reticulation controlleris turned off and the power to the solenoid is removed there is acollapsing field generated by the coil L1 of the solenoid valve 17 b.This field needs to be dissipated and controlled, otherwise it mightpass back through the triac and cause spikes on the conductor 25. Thecollapsing field is captured via inductor L2 and capacitor C4 and isthen shorted out via the flyback diode D6. The result of this circuit isthat once the triac 43 a or 43 b is actuated, the coil L3 or L1 ofsolenoid 17 a or 17 b latches hard on, and will not release untiloperational voltage and current ceases to flow through the half waverectifier 35 a or 35 b, and until the reactive current in the coils L3and L4 or L1 and L2 is dissipated. This process is completed withinthree AC half cycles, with the component values shown.

The negative side 13 a of the decoder circuit 13 works in an identicalfashion.

As can be seen with this arrangement, the two solenoid valves 17 a and17 b may be independently operated from the irrigation controller 15through the single conductor 25 and the return conductor 19. Without theuse of the duplex encoder/decoder pair, it would be necessary to providethree separate conductors between the two solenoid valves 17 a and 17 b,the output connections 2 and 3 and common connection C of the irrigationcontroller 15.

In addition to this, if both signals are on then full wave AC flows, andthis results in the decoder seeing both valves as being active and turnsthem on. This is an important feature as it means that it is possible toset up retrofits using a master valve and a station valve. Other deviceson the market do not allow this type of interface.

Use of the duplex encoder/decoder pair offers significant advantages intwo areas. The first is a cost saving where exceptionally long runs ofwiring are required between an irrigation controller and solenoidvalves. However, the major advantage is that apart from any effortrequired to connect the encoder and decoder circuits, existingirrigation systems can be extended by adding a watering zone, withouthaving to dig up existing wiring or dig trenches to add further wiringto provide connection between the new solenoid valve and the existingirrigation controller. That is, the additional sprinkler unit is merelyadded to an existing unit and the encoder and decoder circuits areinstalled.

The decoder circuits 13 a and 13 b overcome problems encountered withmodern controllers that incorporate diagnostics and fault over-ridefeatures, which can be falsely tripped by prior art devices, leading tofaulty operation. The turn-on delay implemented in the decoder circuit13 provides a soft start mechanism so that the two valves beingcontrolled don't electrically change quickly and hence this limitsinrush current and the chances of the electronic fuse in the controllerfrom tripping. The turn-off delay implemented in the decoder circuit 13provides a soft shutdown mechanism at the valve end that does not letthe collapsing energy field in the coil pass back to the control systemthus eliminating random electronic fuse tripping. The decoder circuitalso provides a booster mechanism that acts like a capacitive dischargesystem, which means that the inrush current to pull a valve coil in islowered and the holding current is all that needs to be handled by thecabling. The effect of this is to help in a situation when cable and theconnections are failing or not up to scratch. Also provided is Lightningprotection at the valve and also for the cabling back to the irrigationcontroller, and on the multiplex control cable and Electronic fuseprotection to limit fault conditions at the decoder end causing damageto the controller or the cabling.

In a preferred embodiment, the components contained within both theencoder 11 and the decoder 13 should be encapsulated in a watertight,waterproof housing so that the decoder circuit 13 may be buried in theground, along with the associated solenoid valves 17 a and 17 b. Theencoder is then disposed adjacent to the control unit.

In yet a further embodiment, the positive half decoder circuit 13 b ornegative half decoder circuit 13 a could be built into or encapsulatedwith a solenoid coil. In this manner either would operate normally on asupplied 24 volt AC supply, or one of each could be used with an encodercircuit 11 as described.

The embodiment presented has been designed to be most economical andcost effective. Changes could be made to achieve the same result, forexample by changing the triac to a silicon controlled rectifier or othertransistor based circuit, or even a mechanical relay, and using adifferent circuit to achieve the turn-on timer function such as a 555timer, a Schmitt trigger CMOS circuit or even a microprocessor, althoughthese are considered to be clumsy implementations.

It should be appreciated that the scope of the invention is not limitedto the embodiment described herein. In particular, the invention hasapplication in other areas besides use in automatic sprinkler systems.The invention would prove equally suitable for use in any applicationutilizing one or more AC supplies and one or more AC loads which areoperable on half wave rectified power supplies.

Thus, there is shown and described a unique design and concept of duplexencoder/decoder unit for alternating current systems. While thisdescription is directed to a particular embodiment, it is understoodthat those skilled in the art may conceive modifications and/orvariations to the specific embodiments shown and described herein. Anysuch modifications or variations which fall within the purview of thisdescription are intended to be included therein as well. It isunderstood that the description herein is intended to be illustrativeonly and is not intended to be limitative. Rather, the scope of theinvention described herein is limited only by the claims appendedhereto.

We claim:
 1. A duplex encoder/decoder pair for interfacing a firstcurrent source and a second current source with a first load and asecond load over a single conductor, comprising an encoder portionhaving a first input for connection to said first current source, and asecond input for connection to said second current source, and an outputfor connection to the single conductor, and comprising a decoder portionhaving an input for connection to the conductor, a first output forconnection to a first load and a second output for connection to asecond load, where the encoder portion is adapted for selectivelyconducting current from the first encoder input to the encoder outputand alternatively the encoder output to the second encoder input, andthe decoder portion is adapted for selectively conducting current onlyfrom the decoder input to the first decoder output and alternativelyfrom the second decoder output to the decoder input, the decoder portionalso incorporates a first switching circuit between said input and saidfirst output, interfaced with a first turn on delay timer to time out apredetermined period before operating said first switching circuit, anda second switching circuit between said input and said second output,interfaced with a second turn on delay timer to time out a predeterminedperiod before operating said second switching circuit, the first decoderoutput and the second decoder output each including a turn-off delaycircuit, each turn-off delay circuit comprising a diode and capacitorconnected in parallel, connected in series with an inductor, which whenin circuit is connected across the load which is connected to therelevant output.
 2. A duplex encoder/decoder pair as claimed in claim 1wherein the value of the capacitor and the value of the inductor areselected to delay turn off of the relevant output by holding the outputhigh for a period of at least 0.015 seconds.
 3. A duplex encoder/decoderpair as claimed in claim 1 wherein the first switching circuit and thesecond switching circuit each use a low gate current triac.
 4. A duplexencoder/decoder pair as claimed in claim 3 wherein the low gate currenttriac is capable of switching with gate currents as low as 5 mA.
 5. Aduplex encoder/decoder pair as claimed in claim 3 wherein the low gatecurrent triac can switch in all four quadrants.
 6. A duplexencoder/decoder pair as claimed in claim 1 wherein the first turn ondelay timer to time out a predetermined period before operating saidfirst switching circuit and the second turn on delay timer to time out apredetermined period before operating said second switching circuit areeach a transistor based RC timer circuit.
 7. A duplex encoder/decoderpair as claimed in claim 1 wherein the first turn on delay timer and thesecond turn on delay timer each provide a turn on delay of at least 0.1seconds.
 8. A duplex encoder/decoder pair as claimed in claim 7 whereinthe turn on delay is about 0.5 seconds.
 9. A decoder half for a duplexdecoder, for use with a duplex encoder, said duplex decoder half havingan input connecting to a half wave rectifier having a half waverectified output, said half wave rectified output leading to a switchingcircuit interfaced with a turn on delay timer to time out apredetermined period before operating said switching circuit on saidhalf wave rectifier passing current at an operational voltage, theoutput of the switching circuit connecting to an output for connectingto a load and to a turn-off delay circuit comprising a diode andcapacitor connected in parallel, connected in series with an inductor,which is connected across the load.
 10. A control circuit as claimed inclaim 9 wherein the value of the capacitor and the value of the inductorare selected to delay turn off of the relevant output by holding theoutput high for a period of at least 0.015 seconds.
 11. A controlcircuit as claimed in claim 9 wherein the turn on delay timer provides aturn on delay of at least 0.1 seconds.
 12. A duplex encoder/decoder pairas claimed in claim 11 wherein the turn on delay is about 0.5 seconds.13. A duplex encoder/decoder pair as claimed in claim 9 wherein the turnon delay timer to time out a predetermined period before operating saidswitching circuit is a transistor based RC timer circuit.
 14. A duplexencoder/decoder pair as claimed in claim 9 wherein the first switchingcircuit and the second switching circuit each use a low gate currenttriac.
 15. A control circuit for a solenoid, said control circuit havingan input connecting to a half wave rectifier having a half waverectified output, said half wave rectified output leading to a switchingcircuit interfaced with a turn on delay timer to time out apredetermined period before operating said switching circuit on saidhalf wave rectifier passing current at an operational voltage, theoutput of the switching circuit connecting to an output for connectingto a load in the form of said solenoid, said output having a turn-offdelay circuit comprising a diode and capacitor connected in parallel,connected in series with an inductor, which when in circuit is connectedacross the load.
 16. A control circuit as claimed in claim 15 whereinthe value of the capacitor and the value of the inductor are selected todelay turn off of the relevant output by holding the output high for aperiod of at least 0.015 seconds.
 17. A control circuit as claimed inclaim 15 wherein the turn on delay timer provides a turn on delay of atleast 0.1 seconds.
 18. A duplex encoder/decoder pair as claimed in claim17 wherein the turn on delay is about 0.5 seconds.
 19. A duplexencoder/decoder pair as claimed in claim 15 wherein the turn on delaytimer to time out a predetermined period before operating said switchingcircuit is a transistor based RC timer circuit.
 20. A duplexencoder/decoder pair as claimed in claim 15 wherein the first switchingcircuit and the second switching circuit each use a low gate currenttriac.